Fragile X Syndrome

Fragile X Syndrome (FXS) is a hereditary disorder of the X chromosome. FXS is the most common cause of inherited mental retardation.

Causes

FXS is caused by mutations of the FMR1 gene. These mutations interfere with the normal development of certain parts of the brain and body.

Risk Factors

A risk factor is something that increases your chances of getting a disease or condition. The main risk factor for FXS is having a parent with an FMR1 mutation. These mutations vary in degree. People who inherit a minor mutation, which is sometimes called a permutation, do not develop the symptoms and signs of FXS. However, children of parents with FMR1 permutations are at risk of inheriting a fully mutated FMR1 gene severe enough to cause symptomatic FXS. If a woman is an asymptomatic carrier of an FMRI permutation, each child of hers has a 50% chance of inheriting that gene. Of the children that inherit that gene, boys are much more likely to develop symptoms than girls. In addition, each subsequent generation tends to have worse mutations and a higher risk of FXS than the previous one.

Symptoms

The number and severity of symptoms varies widely. Symptoms tend to be less frequent and milder in females. Symptoms can include:
  • Mental impairment
    • Impairments range from learning disabilities to mental retardation
  • Behavioral difficulties, including:
    • Attention deficit and hyperactivity disorder (ADHD)
    • Anxiety
    • Unstable moods and emotional outbursts
    • Aggressive behavior
    • Extreme shyness (particularly in girls)
  • Autistic behaviors
  • Physical problems and abnormalities, including:
    • Long face with protruding jaw
    • Large, protruding ears
    • Flat feet
    • Hyper-extended joints
    • High-pitched voice and enlarged testes in males after puberty
    • Mitral valve prolapse
    • Seizures

Diagnosis

The doctor will ask about symptoms and medical history, and perform a physical exam. FXS may be suspected if a child has:
  • Physical, cognitive, or emotional symptoms of FXS
  • Unexplained developmental delays or mental retardation
The diagnosis can be confirmed by a DNA blood test.

Treatment

There is no cure for FXS. Treatment is aimed at controlling symptoms. Treatment may include:
Medication Medications used to treat symptoms of FXS include:
  • Stimulants (such as Ritalin) and other medications to treat hyperactive behavior
  • Psychotherapeutic drugs (such as Prozac) to help control:
    • Anxiety
    • Aggression
    • Emotional outbursts
  • Anti-convulsants (such as carbamazepine) to control seizures
Educational StrategiesSpecific educational strategies depend on the degree of developmental delays and/or mental retardation. Educational strategies include setting a stable educational environment for the patient that includes:
  • School work that only requires a short attention span
  • Minimal distractions
  • Predictable activities and classroom routine
  • Close communication between parent and school
  • Emphasis on functional life skills

Prevention

There are no known ways to prevent FXS once a person is born. If you have FXS or risk factors for FXS, you can talk to a genetic counselor before deciding to have children.